This invention relates generally to inspection of integrated circuit devices on a silicon wafer in a probe station, and more particularly to an adapter and probe card holder for energizing and probing a silicon wafer in an inverted position for analysis of backside emissions.
Probe stations are well known as a means for wafer probing and failure analysis investigations of a device under test (DUT) on a silicon wafer. A probe station generally involves a platform for mounting probing apparatus such as a probe card or probe holders, a moveable chuck for holding the wafer with x, y, z and theta stages for positioning the chuck, and an optic system with video imaging and integrated system software to monitor the progress of the probing and failure analysis on a computer screen. Normally, probing of the device is done from above on the top side of the wafer which faces upwardly, while its opposite (or backside) faces downwardly.
One type of analysis involves energizing the DUT in order to observe infrared emissions from a defect, consisting of overlaying an illuminated device image showing device details with another image of infrared emissions from the energized device. The images are superimposed to determine the location of the defect. Difficulties are encountered with this type of analysis after several layers have been added to the silicon substrate. This problem has led to a similar analysis known as backside emission inspection. Under this procedure, the silicon wafer is inspected from the backside of the wafer, usually in an inverted position. The back of the wafer is first treated to reduce its thickness at the location to be inspected and the backside is illuminated at special frequencies and using special sensors to observe emissions from the backside of the energized device. The precise equipment necessary to illuminate and detect backside emissions is not the subject of the present invention.
The present invention involves the use of a conventional probe station in order to adapt it for backside emission inspection, and probing from the underside of a silicon wafer held in an inverted position, together with various features necessary for backside emission inspection.
Existing apparatus for backside emission testing has required unacceptably long set-up times to adapt and calibrate the probe station to enable probing from the underside of the silicon wafer and to energize the DUT. The probed surface must be planar with respect to the plane of motion of the probing apparatus, (or with respect to the probe card). It would be desirable to have an adapter which is readily and quickly set up for backside emission inspection, and which also can be utilized in a standard probe station, rather than requiring a special probe station.
Accordingly, one object of the present invention is to provide an improved apparatus for inspecting an inverted silicon wafer for backside emissions in a probe station.
Another object of the invention is to provide an improved adapter for holding a silicon wafer in an inverted position in a standard probe station for backside emission testing, together with probing means to energize the wafer from the underside thereof.
Another object of the invention is to provide an adapter for backside emission testing of a silicon wafer with means to establish planarity of the inverted silicon wafer surface with respect to a probe card, by self-leveling of the probe card holder.